Conventional light emitting devices include a light emitting element, such as a light emitting diode chip (LED chip) mounted on a substrate and encased in a protective enclosure that may serve as an optical lens. The substrate provides the structural support required to facilitate handling of the light emitting device during subsequent processes, such as the mounting of the light emitting device on a printed circuit board. The protective enclosure may include a wavelength conversion material that converts at least a part of the light emitted from the light emitting chip to light of a different wavelength. The wavelength conversion material may alternatively be provided as a discrete element between the light emitting chip and the enclosure/lens.
Common techniques for providing a light emitting device as described above include attaching the light emitting element to a wire frame substrate that serves to allow external power connections to the light emitting element, then encapsulating the light emitting element and the portion of the wire frame to which it is attached with a silicone mold. The wire frame may be part of a carrier that includes multiple frames for mounting light emitting elements, such that the encapsulation can be performed for all of the light emitting elements as a single molding process.
In another embodiment, the light emitting element is mounted on a ceramic substrate that includes conductors to which the light emitting element is attached. U.S. Pat. No. 7,452,737, “MOLDED LENS OVER LED DIE”, issued 18 Nov. 2008 to Grigoriy Basin, Robert Scott West, and Paul S. Martin, discloses a ceramic substrate that accommodates multiple light emitting elements, and a mold that forms a lens element over each of the light emitting elements. The ceramic substrate may subsequently be sliced/diced to provide ‘singulated’ light emitting devices that include external connections to the light emitting element on the ceramic substrate.
In another embodiment, the substrate includes cup-like cavities within which the light emitting elements are attached to conductors for coupling the light emitting element to a power source. The light emitting elements are encapsulated by filling the cavities with a low viscosity silicone and curing the silicone. The cavity may be shaped to provide a particular optical effect, and/or a mold may be used to form a desired lens structure above the cup. U.S. Pat. No. 7,214,116, “LIGHT-EMITTING DIODE AND METHOD FOR ITS PRODUCTION”, issued 8 May 2007 to Akira Takekuma, discloses placing a preformed lens atop the silicone within the cup. After curing the silicone, the substrate is diced to provide the singulated light emitting devices.
Each of the above processes requires singulating the light emitting dies, mounting each die on the substrate, encapsulating the dies on the substrate, then slicing/dicing the substrate to singulate the completed light emitting devices. In addition to the additional manufacturing cost and effort associated with the double-handling involved with the intermediate step of mounting the light emitting dies on a substrate, this double-handling process also challenges applications wherein the light emitting die is required to have a particular location with respect to the optics of the enclosing structure. In many applications, if the light emitting element is ‘off-center’ relative to the optics of the enclosing structure, the formed light emitting device may be discarded as ‘failed’ in the manufacturing process, or may pass the manufacturing test and result in a defective product when it is incorporated into the product. For example, in a camera-flash application, if the camera/cell-phone/tablet/etc. produces pictures with non-uniform illumination, the purchaser of the camera/cell-phone/tablet/etc. will likely demand a replacement.
Although fairly simple techniques are available to properly align the substrate with the tool that provides the molded lens structure, such as creating alignment features in each of the substrate and the tool, achieving a correspondingly proper alignment of the light emitting element on the substrate is a more challenging and costly task, requiring, for example, a high-precision ‘pick-and-place’ machine to place each light emitting element at a highly-precise location on the substrate.
In order to avoid the aforementioned double-handling of the light emitting element, technologies have evolved to provide light emitting dies that are self-supporting, and can be handled directly. WO 2013/084155, “FORMING THICK METAL LAYERS ON A SEMICONDUCTOR LIGHT EMITTING DEVICE”, published 13 Jun. 2013 for Schiaffion, Akram, Basin, Munkhol, Lei, and Nickel, and incorporated by reference herein, discloses light emitting elements that have thick metal layers that provide the structural support required for routine handling of the elements, eliminating the need for a supporting substrate. Because the self-supporting chip can be handled without further packaging, it is commonly termed a “Chip Scale Package” (CSP).
However, even though these self-supporting chips do not require a structural substrate, the conventional encapsulation processes still require that these chips be placed on some form of substrate, to allow multiple chips to be encapsulated at the same time, with the accompanying difficulty in assuring alignment of the light emitting chip and the attached lens structure.